What Are Antioxidant Nanozymes?

Among the reactive species or free radicals generated in biological systems, reactive oxygen species (ROS) and reactive nitrogen species (RNS) are well-known. Antioxidant enzymes are essential for scavenging oxygen free radicals; however, they suffer from poor stability.

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To address this limitation, antioxidant nanozymes have been developed to efficiently mimic enzymatic catalytic activity.¹ These nanozymes possess intrinsic enzymatic properties, making them valuable for biomedical applications.

Mechanism of Action

Mimicking Catalase Anti-Oxidative Properties

Artificially developed nanozymes can mimic the activity of natural antioxidant enzymes such as catalase and superoxide dismutase. Catalase can efficiently function as an anti-oxidative enzyme by reducing hydrogen peroxide to release O₂ and water.²

Among various options, cerium-containing nanozymes can perform antioxidant functions similar to catalase. These nanozymes operate like natural enzymes by enabling a reaction between Ce⁴⁺ and hydrogen peroxide, resulting in the release of molecular oxygen and the reduction of Ce⁴⁺ into Ce³⁺ ions. This process allows the nanozymes to replicate the antioxidant properties of catalase.³

Additionally, a ferritin-platinum nanoparticle blend has been found to enhance antioxidant activity by accelerating the conversion of Ce⁴⁺ into Ce³⁺.

Antioxidant Nanozymes: An Efficient Dismutase Alternative

Superoxide radicals are generated as byproducts of human metabolic processes. During natural antioxidant processes, superoxide dismutase catalyzes the conversion of superoxide radicals into hydrogen peroxide, releasing oxygen in the process.

Chemically modified nanozymes with antioxidant properties similar to superoxide dismutase play a crucial role in protecting against oxidative stress. Transition-metal-based nanozymes have shown high efficiency in mimicking the antioxidant activity of dismutase.

In transition metal-based nanozymes, changes in the oxidation states of the metals create oxygen vacancies within the lattice, which are essential for antioxidant reactions. These vacancies enable the nanoparticles to absorb or release oxygen as needed.⁴ Transition metals such as gold, silver, platinum, and copper have been widely used in developing antioxidant nanozymes to replicate dismutase activity.

How Size Affects the Activity of Nanozymes

The size of the material is a crucial factor in determining the antioxidative efficiency of nanozymes. Researchers observed that nanozymes with 4.2 nm nanoparticles demonstrated a faster and more efficient free radical reduction process compared to those with 14 nm nanoparticles.⁵

Studies have shown that the size of transition metal-based nanozymes, such as cerium oxide nanoparticles, is inversely related to their ability to mimic natural antioxidative properties, such as dismutase-like activity. As particle size decreases, the Ce³⁺/Ce⁴⁺ ratio on the particle surface increases, creating more oxygen vacancy defects. These vacancies are essential for antioxidative enzymatic activity, as they provide additional active sites for reactions with substrates. This indicates that smaller nanoparticles exhibit higher antioxidative activity.⁶

Another important factor influencing antioxidative properties is the morphology of the nanomaterial. Nanozymes with a high specific surface area offer more active sites, significantly enhancing antioxidative enzymatic activity. Nanoclusters, which have a much larger specific surface area than regular nanoparticles, show greater efficacy in reducing oxidative stress. Additionally, properties like low surface energy have been found to promote antioxidative behavior further.

Types of Antioxidant Nanozymes

Researchers have developed various types of antioxidant nanozymes based on different materials and nanoparticles.

Metal- and metal-oxide-based nanozymes have been especially valuable in applications such as fuel cells and electrocatalysis, offering exceptional stability and robustness, along with tunable physiochemical properties.⁷

Experts have used surface modification techniques to enhance the efficiency and biocompatibility of metal-based nanozymes, making them suitable for applications in the chemical industry and biomedicine.

Additionally, metal oxide nanoparticles, like MnO and NiO nanoflowers, enhance the antioxidant enzymatic activity of nanozymes. Metal and metal oxide nanoparticles are particularly effective for protection against oxidative stress due to their high surface area and stability in oxidative environments.⁷

Another major type of antioxidant nanozymes includes carbon-based nanozymes, such as fullerenes, graphene, and quantum dots. Carbon-based nanozymes are favored for their unique electronic configuration, which enables superior performance across a wide range of temperatures and pH levels, making them highly suitable for biosensing applications.⁸

Among various carbon-based nanozymes, carbon dots (CDs), typically smaller than 10 nm, have demonstrated high activity in scavenging reactive oxygen and nitrogen species (RONS). Their small size enhances their enzymatic capabilities, as confirmed by experimental results showing the significant potential of CD-based nanozymes in a range of applications. CDs are particularly promising for antioxidant uses due to their nontoxic nature and excellent thermal stability.⁹

Applications of Antioxidant Nanozymes

Biomedical Research

The tunable properties and enzyme-mimicking capabilities of nanozymes, especially for managing oxidative stress and treating diseases, have made them widely popular in biomedical research. Palladium-based nanozymes are being extensively studied for biosensing applications, while iron oxide, gold, and platinum nanozymes are top choices for cancer therapy and treatment of infectious diseases.

A major concern in biomedical research is the regulation of intercellular ROS levels, as elevated ROS levels are strongly linked to the development of nervous system diseases. Doping nanozymes with specific particles endows them with ROS-scavenging properties, making them a key choice for neuroprotection.¹⁰

Given these biomedical applications, the development of nanomaterial-based artificial enzymes offers a fresh perspective for catalysis-driven biomedical research aimed at supporting human health.

Food Safety and Preservation

Nanozymes also serve as key antioxidants in the food industry. Naturally occurring enzymes often cannot withstand harsh operating conditions, making nanozymes a priority for researchers globally.

Nanozyme-based systems are widely used to detect contaminants and harmful bacteria in food products. For heavy metal detection, researchers have developed a graphene-oxide nanozyme screen coated with bismuth film, which is highly effective in detecting cadmium and lead ions.¹¹

Additionally, nanozyme-based techniques for identifying food adulterants are gaining popularity in the food industry. Silver-based nanozymes can detect melamine in dairy products without cross-reactivity. Carbon dot-based nanozymes, known for their strong antioxidant properties and high biocompatibility, are used for both food preservation and contaminant detection, as they inhibit bacterial activity and prevent spoilage.¹²

Skin Care and Cosmetics

Nanozymes are also used in cosmetics. Gold nanozymes combined with gallic acid exhibit unique antioxidant properties that help skin appear younger and more refreshed.¹³

Boron- and phosphorus-based ternary nanozymes possess anti-inflammatory properties and are used in cosmetic products to protect skin from oxidative stress. The anti-aging benefits provided by nanozymes make them a valuable choice for the cosmetics industry.

Challenges and Future Directions for Nanozyme Development

Nanozymes have shown potential in various research fields, though biotoxicity remains a challenge for scalability. Researchers are working to address toxicity and compatibility concerns for certain nanozymes, with a strong focus on sustainable development for industrial applications.

These efforts indicate confidence in the future of nanozymes in biomedical applications and suggest possible growth in the nanozyme market.

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References and Further Reading

1. Liu, X., et al. (2024). Advances in antioxidant nanozymes for biomedical applications. Coordination Chemistry Reviews. https://doi.org/10.1016/j.ccr.2023.215610
2. Haider, M., et al. (2021). Overproduction of ROS: underlying molecular mechanism of scavenging and redox signaling. Biocontrol Agents and Secondary Metabolites. https://doi.org/10.1016/B978-0-12-822919-4.00014-4
3. Zeng, L., et al. (2020). In vivo regenerable cerium oxide nanozyme-loaded pH/H2O2-responsive nanovesicle for tumor-targeted photothermal and photodynamic therapies. ACS Applied Materials & Interfaces.  https://doi.org/10.1021/acsami.0c19074
4. D’Angelo, A., et al. (2016). Oxygen uptake of Tb–CeO2: Analysis of Ce3+ and oxygen vacancies. The Journal of Physical Chemistry C. https://doi.org/10.1021/acs.jpcc.6b04063
5. Shlapa, Y., et al. (2022). Cerium dioxide nanoparticles synthesized via precipitation at constant pH: Synthesis, physical-chemical and antioxidant properties. Colloids and Surfaces B: Biointerfaces. https://doi.org/10.1016/j.colsurfb.2022.112960
6. Zhao, H., et al. (2021). Superoxide dismutase nanozymes: an emerging star for anti-oxidation. Journal of Materials Chemistry B. https://doi.org/10.1039/D1TB00720C
7. Jin, L., et al. (2019). PdPt bimetallic nanowires with efficient oxidase mimic activity for the colorimetric detection of acid phosphatase in acidic media. Journal of Materials Chemistry B. https://doi.org/10.1039/C9TB00730J
8. Singh, N. (2021). Antioxidant metal oxide nanozymes: role in cellular redox homeostasis and therapeutics. Pure and Applied Chemistry. https://doi.org/10.1515/pac-2020-0802
9. Ding, H., et al. (2021). Carbon-based nanozymes for biomedical applications. Nano Res. https://doi.org/10.1007/s12274-020-3053-9
10. Gao, F., et al. (2023). Carbon dots as potential antioxidants for the scavenging of multi-reactive oxygen and nitrogen species. Chemical Engineering Journal. https://doi.org/10.1016/j.cej.2023.142338
11. Wei, M., et al. (2021). Chemical design of nanozymes for biomedical applications. Acta biomaterialia. https://doi.org/10.1016/j.actbio.2021.02.036
12. Payal, A. et al. (2021). A Review on Recent Developments and Applications of Nanozymes in Food Safety and Quality Analysis. Food Anal. Methods. https://doi.org/10.1007/s12161-021-01983-9
13. Cui, F., et al. (2023). Fe/N-doped carbon dots-based nanozyme with super peroxidase activity, high biocompatibility and antibiofilm ability for food preservation. Chemical Engineering Journal. https://doi.org/10.1016/j.cej.2023.145291
14. Kim, J., et al. (2020). Au nanozyme-driven antioxidation for preventing frailty. Colloids and Surfaces B: Biointerfaces. https://doi.org/10.1016/j.colsurfb.2020.110839

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